The performance of a ramjet powered device, such as a missile, is dependent on the size, weight and performance of the individual components of the missile as well as the interaction between these components when integrated into an overall “system”. In general, if the performance of an individual component is increased and/or the size and/or weight of the individual component is reduced, the overall performance of the ramjet powered device will be improved.
The component that has the most impact on the design and performance of the ramjet engine and the device it powers is the combustor. As those skilled in the art will appreciate, traditionally combustor designs that feature short combustor lengths typically require high blockage instream flameholders in the combustor that cause large pressure losses and therefore reduce propulsion performance. In contrast, long combustors without the relatively large instream flameholders typically increase the overall size and weight of a ramjet powered device and as such, effectively reduce the range and/or payload capacity of the ramjet powered device.
Classically designed ramjet powered missiles are known to employ combustors with instream bluffbody flameholders, which resulted in a combustor length-to-diameter (L/D) ratio of about 3.0. To accelerate these classically designed ramjets to their supersonic operational speeds a strapped-on external rocket booster was used. Due to the external booster these designs were relatively bulky.
The relative bulk and high weight of classically designed ramjet missiles prompted development of more streamlined designs that were thought to be more cost effective and have longer ranges and/or greater payload capacity. One such design, the integral rocket ramjet (IRR), employs an integral rocket booster, housed inside the ramjet combustor, for accelerating the missile to its ramjet takeover speed, which is typically about Mach 1.5 or higher. With the combined, dual use, rocket/ramjet combustor the liquid fueled IRR is typically sized with a combustor L/D ratio of about 5.0 creating a relatively long and heavy propulsion system.
A combination of the classical and streamlined designs resolved some of the problems with the prior ramjet powered devices, but the combustor required an L/D ratio of about 3.0, was still relatively long and too heavy. Furthermore, significant pressure losses were associated with the instream flameholders and as such, thrust performance and mission capability were degraded. Accordingly, there remains a need in the art for a ramjet engine having an improved combustor.